Laser scanners containing torsion oscillators are known, although not widely used in scanning systems. U.S. Pat. Nos. 4,762,994 to Byerly et al., 5,543,956 to Nakagawa et al. and 5,767,666 to Asada et al. are illustrative examples of such laser scanners. An illustration of a galvanometric torsion oscillator is shown in the '994 patent. (The term galvanometric is believed to be a reference to coils on the turning member operated in the manner of a common galvanometer.)
The torsion oscillator functions as a laser scanner when a laser beam is directed at an oscillating mirror surface of the device. Such a device replaces the much bulkier rotating polygonal mirror widely used in laser printers and copiers. Torsion oscillators also have other applications, such as to drive a clocking device, in which a mirror would not be used.
Because the oscillations of the plate are relatively rapid during a scanning process, variations or distortion of the motion of oscillating plate can occur due to the influence of external air currents. Such disturbances from external air currents result in jitter of the laser beam image scanned across the photoconductor in a laser printer. Dust accumulation on an oscillating plate or rotating mirror scanning device may also cause variations or distortions in the motion of the mirror and deterioration of intensity of the laser beam image scanned across the photoconductor in a laser printer.
Accordingly, there is a need for improved oscillating plate systems that are not adversely affected by stray air currents.